1. Field of the Invention
The present invention relates to a lithographic apparatus, and a mechanism.
2. Description of the Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g., including part of, one, or several dies) on a substrate (e.g., a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Conventional lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
In the operation of a lithographic apparatus, different objects to be used or processed are taken from one location to another in the apparatus, while such objects previously have been placed or stored in the apparatus. In the placement or storage of an object, care must be taken that the object is held in a predetermined location and/or spatial orientation such that a handler may contact the object without human intervention, hold it, take it to another location, and place it at the other location in a predetermined way and/or spatial orientation. Before, during or after taking an object from one location to another, a fixing of the object may be required to prevent the object from an inadvertent displacement.
As an example, in a known lens or system of lenses of a lithographic apparatus, different thin, generally ring-shaped blades (also termed: cleanup aperture blades) may be used defining different openings for light passing through the lens or system of lenses. Such blades are stored in a cassette containing several blades having different openings. A specific blade for obtaining a specific opening may be taken from the cassette by connecting a gripper of a handler to the blade, the handler removing the gripped blade from the cassette, transporting the blade to the lens or system of lenses, and placing it there.
The blades are fixed in adjacent compartments of the cassette by providing the blades with hooks, and hanging the blades with the hooks engaging in holes provided in storage compartments of the cassette, or by hanging the blades on hooks provided in the storage compartments of the cassette, where the hooks engaging in holes provided in the blades.
While taking a blade from the cassette for a placement of the blade in the lens or system of lenses, or storing a blade in the cassette, the other blades need to maintain their position in the cassette, which is guaranteed by the hook and hole fixing of the blades. Thus, any change of cassette position will not lead to a change of the position of the blades remaining in the cassette.
It is, however, a cumbersome operation to remove a blade from, or to insert a blade into the cassette. Taking a blade from a hook in a cassette compartment by a handler, or placing a blade on a hook in a cassette compartment by a handler, may require complex movements of the cassette and/or the handler, which is time-consuming, the more so since the movements cannot be performed with high speed or high acceleration to prevent the blades held on the hooks in the cassette to displace relative to the hooks.
A similar situation exists in the storage, or temporary storage, and holding or fixing of other elements in a lithographic apparatus, for example diffractive optical elements, wafers, substrates, etc.